The present invention relates to an insulator surface layer such as an oxide and a fluoride. The present invention further relates to solid state electronic devices having insulators.
A solid state electronic circuit such as a semiconductor integrated circuit is constructed of semiconductor material, metal, insulators, and other materials, which are processed into fine patterns and are stacked.
Insulators are often composed of a silicon oxide thin film or a thin film of amorphous structure containing boric acid, phosphorous and other elements, with silicon oxide as its main component. These thin films are usually formed as layers on a substrate (including directly on other layers that are on the substrate) by silicon thermal oxidation or chemical vapor deposition (CVD), plasma CVD, and sputtering deposition.
For example, an insulating film used for an insulator between metal wirings of a semiconductor integrated circuit often has a film of SiO.sub.2 as its main component, which is formed by the CVD using a gas such as SiH.sub.4 and N.sub.2 or plasma CVD. The insulator film may be approximately 1 .mu.m thick. Then, usually, subsequent to the formation of wiring via-holes, and other patterns by the lithographic process and etching process, the next layer which is a metal layer for wirings is stacked by the CVD method, sputtering deposition or the like, and through subsequent lithographic and etching processes, fine metal wirings are formed. In the stacked structure of a semiconductor integrated circuit formed in such a series of processes, rarely it has been attempted to improve intentionally the modification of the film quality of the surface insulator film layer or interlayer insulator film. The insulator film as deposited is used as it is.
Also, a silicon oxide thin film of 10-20 nm thick and mostly formed by thermal oxidation is used for the gate insulator film for the silicon MOS type transistor. In this case, too, the thin film is used as it has been deposited without any particular improving modification treatment for improving the property of the silicon oxide film significantly with the exception of the simple treatment of annealing.
As another example, there is a capacitor insulator film for a memory device of the memory integrated circuit and others, and in recent years, in order to intensify the electrostatic capacity thereof, the silicon oxide film is used in layers with the silicon nitride film having a large dielectric constant.
For the insulator film of a semiconductor integrated circuit as described above, the insulator film deposited by thermal oxidation, CVD or the like is used as it is without any particular surface treatment before the present invention.
A technique for forming an insulator film for a semiconductor integrated circuit is explained in detail in S. M. Sze ed, VLSI Technology, Second Edition (McGraw-Hill, New York, 1988) pp. 98-140 and 233-271, for example.
In the above-mentioned conventional technique, insulator films of SiO.sub.2 and others are used as formed by thermal oxidation or CVD. In the case of the thermal oxidation formed SiO.sub.2 film, its density is usually approximately 2.2-2.3 g/cm.sup.3, for example, and it is known that such SiO.sub.2 film is susceptible to transmission of molecules of H.sub.2 O, O.sub.2 H.sub.2 and others and atoms dissociated therefrom, which often leads to a problem that the oxidation, corrosion, and other degradations of the metal wirings are caused by the water and other molecules thus transmitted. In contrast, a SiO.sub.2 film formed by plasma CVD is in general high in its density and is highly capable of preventing the transmission of water and other molecules. However, in the plasma CVD formed film, a considerable value of H is contained to often result in the film expansion, cracking, and production of other defectives due to the dissociation of the contained H at the time of thermal treatment.
Also, the relative dielectric constant of the SiO.sub.2 film formed by silicon thermal oxidation and others is 3.9-4.0, and since this value is insufficient, a multi-layer film, in which the Si.sub.3 N.sub.4 film or Ta.sub.2 O.sub.5 film having a greater dielectric constant is stacked with the SiO.sub.2 film, is used as an insulator film for the charge storage capacitor of the random access memory device. The dielectric constant of the SiO.sub.2 film is small, and the capacity of the capacitor is also small when made by the SiO.sub.2 film alone.
Further, the SiO.sub.2 film is formed by thermal oxidation or CVD is easily etched by rare fluorine acid or its surface is reduced by the irradiation of H or rare gas ions, and tends to be Si rich.